The present invention relates to a method for manufacturing a hard disk read/write unit having micrometric actuation.
As is known, hard disks are the most commonly used data storage solution. Consequently, they are produced in very large volumes, and the maximum density of data storage is increasing year by year. Hard disks are read and written on by actuator devices, the general structure whereof is shown in FIGS. 1 and 2, and is described hereinafter.
In particular, FIG. 1 shows an actuator device 1 of a known rotary type, which comprises a motor 2 (also known as a xe2x80x9cvoice coil motorxe2x80x9d) secured to a support body 3, which is generally known as an xe2x80x9cE-block,xe2x80x9d owing to its xe2x80x9cExe2x80x9d shape in lateral view (see FIG. 2). The support body 3 has a plurality of arms 4, each supporting a suspension 5 formed by a cantilevered plate. At the end of each suspension 5 opposite to the support body 3, each suspension 5 supports an R/W transducer 6 for reading/writing, which, in an operative condition, is disposed facing a surface of a hard disk 7, such that the R/W transducer 6 can perform roll and pitch movements to follow the surface of the hard disk 7. To this end, the R/W transducer 6 (also known as a xe2x80x9cpicosliderxe2x80x9d or xe2x80x9csliderxe2x80x9d) is bonded to a coupling 8 (also known as a xe2x80x9cgimbalxe2x80x9d). The gimbal 8 is generally formed from the suspension 5 itself and comprises, for example a rectangular plate 8a, cut on three and a half sides from a plate of the suspension 5, and having a portion 8b connected to the suspension 5 to allow bending of the plate 8a by the weight of the R/W transducer 6 (see FIG. 3).
At present, the maximum track density of hard disks is approximately 5000 tracks per inch (TPI), but it is expected that in the near future, a density of at least 25,000 TPI can be achieved. This is equivalent to a distance between tracks of approximately 1 xcexcm and a tracking accuracy better than 0.1 xcexcm.
These density levels cannot be obtained by simply improving the present technology, owing to the existing mechanical problems (e.g. resonance of the positioning arms and low frequency effects). It has thus been proposed to use a double actuation stage having a rougher first actuation stage, with the motor 2 moving an assembly formed by the support body 3, the suspension 5 and the R/W transducer 6 across the hard disk 7 during the tracking, and a second actuation stage performing a finer control of the positioning of the R/W transducer 6. Two solutions have been proposed hitherto: (1) millimetric actuation, where the suspension 5 or the support body 3 are adjusted to control in a millimetric manner the position of the suspension 5, and (2) micrometric actuation, where the position of the R/W transducer 6 is controlled with respect to the suspension 5 through a microactuator interposed between the R/W transducer 6 and the suspension 5. The micrometric solution is shown in FIG. 3, which is an exploded view of the end of the suspension 5, the gimbal 8, the R/W transducer 6 and a rotary-type microactuator 10. The microactuator 10 is controlled by a signal supplied by control electronics, on the basis of tracking errors.
The millimetric solution has the disadvantage that it causes considerable consumption, cannot be obtained by batch production processes, and does not permit high accuracy, and thus does not allow very high density disks to be read. However these problems are solved by the micrometric solution, to which the present invention therefore relates.
In order to manufacture the microactuator 10, different solutions have been proposed, based on electrostatic, electromagnetic and piezoelectric principles. Electrostatic microactuators are generally of a rotary type and comprise two basic elements: (1) a stator secured to the gimbal 8, and (2) a rotor freely movable with respect to the stator and secured to the R/W transducer 6. On the other hand, electromagnetic microactuators substantially comprise variable reluctance micromotors having windings, the purpose of which is to generate a magnetic field attracting a magnetic core. The proposed electromagnetic microactuators are also of the rotary type, since these have greater resistance to impacts than linear microactuators. Microactuators of the piezoelectric type use the piezoelectricity of specific materials in order to obtain movement of a mobile part with respect to a fixed part, and are generally of the linear type.
Microactuators are currently made of two materials: (1) polysilicon inside a suitably excavated wafer (see, e.g., European Patent Application No. 97830556.3 filed on Oct. 29, 1997 in the name of the same applicant); and (2) metal generally grown galvanically on a semiconductor material wafer (see, e.g., the article xe2x80x9cMagnetic Recording Head Positioning at Very High Track Densities Using a Microactuator-Based, Two-Stage Servo Systemxe2x80x9d by L. S. Fan, H. H. Ottesen, T. C. Reiley, R. W. Wood, IEEE Transactions on Industrial Electronics, Vol. 42, No. 3, June 1995).
In both cases, problems exist in that when assembling the read/write head to the microactuator 10 and forming the connections with the control circuitry, displacement of the various components can occur, and/or the suspended structures can stick. In addition, stresses can arise to create conditions of fragility of the structure.
Accordingly, one advantage of the invention is to provide a method of manufacturing a read/write unit including at least the microactuator and the read/write transducer, the method using conventional microelectronics manufacturing techniques, and as far as possible, reducing offset and residual stresses.
According principles of the present invention, a method is provided for manufacturing a hard disk read/write unit having micrometric actuation. In an embodiment of the invention, the method comprises forming an integrated device including a microactuator securable to a suspension device, forming an immobilization structure for the microactuator, and securing a read/write transducer to the microactuator after forming the immobilization structure. The method can further comprise removing the immobilization structure after securing the transducer to the microactuator. The securing of the transducer to the microactuator comprises forming a securing flange rigid with the microactuator and bonding the transducer to the securing flange. The method further comprises forming electrical connections between the transducer and the integrated device.